Effect of asymmetric cold rolling on the microstructure, texture, and mechanical properties of the AZ91 alloy

Abstract

In this study, the effect of asymmetric cold rolling on microstructure, texture, and mechanical properties of AZ91 magnesium alloy investigated. Optical microscopy (OM), scanning electron microscopy (SEM), x-ray diffraction (XRD), tensile, and hardness tests performed. The homogenization process significantly increased the grain size of the as-cast sample. During 8% rolling, continuous dynamic recrystallization (CDRX) mechanism resulted in a relatively sharp drop in average grain size. The results indicated that the formation of extension twins during rolling led to a rotation of primary oriented grains toward texture. After 15% deformation, the created basal texture with the intensity of 4.6 mrd has almost 10-degree deviation from the normal direction. With increasing the rolling reduction, the hardness increased due to increasing the fraction of twins and intensity of basal texture. The 8% deformed sample had the maximum tensile strength and microhardness owing to the saturation of twins as well as the absence of microcracks in the microstructure. Findings showed that the as-homogenized and 8% rolled samples had the highest and lowest inhomogeneity factor (18.5 and 10.6), respectively. The failure mode was a mixture of cleavage and ductile fracture. With increasing the thickness reduction, the cleavage mode became severe due to the formation of microcracks.